It's impossible to say with any accuracy whether or not you should "risk it". Numbers given out in this forum are generalizations. So many factors go into this it's impossible for anyone to say. How are they testing, how thorough is the testing, etc. Many labs will be able to see if you diluted your urine sample by drinking lots of water the day of, for example. However, whoever is testing may not be paying for such a service. If you use detox, they can test for that too, as long as someone is paying for it. However, based on what you've said, you should be fine. If you only smoke about once a month, I imagine whatever you smoke will be cleared out fairly rapidly.